While they remain supportive of Khloé, tensions are likely simmering between the sisters and Thompson, 27. On Tuesday, a source told PEOPLE that Kim, 37, and her husbandKanye West, 40,are upsetwith the NBA star for his alleged infidelity.

“They both feel Khloé has gone through so much and that she deserves being happy,” said the source. “They can’t believe that Tristan has been going behind everyone’s back. They find his behavior disgusting.”

“Kim is very protective of Khloé and is especially upset,” added the source. “She can’t imagine Khloé will stay with Tristan, but will support her sister either way.”

Tristan and Khloé.

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Thus far, the future of Khloé and Thompson’s relationshipremains unclear,and sources have told PEOPLE the new mom is choosing to focus on her newborn.

“Khloé really wants to be able to forgive and trust Tristan again and have the life she hoped to have with him,” one insider told PEOPLE on Monday. “She doesn’t know if she’ll be able to do that, but that’s the goal. She loves the life they had, she loves the baby they have together, and she still loves the dream of being a family together. If she can find a way to rebuild with Tristan, she will.”